Geochemistry and Assessment of Toxic Elements Recovery in Parvadeh Coal Mine, Tabas

Parvadeh coalfield with an area of 1200 km2 is one of the largest coalfields in East-Central Iran. The coal-bearing clastic rocks of the coalfield belong to Ghadir Member of the Upper Triassic Naiband Formation and could be classified as bituminous coal, containing low volatile, high ash and medium to high sulfur. Pyritic sulfur is the main form of sulfur in the Parvadeh coals. Quartz, illite, kaolinite, pyrite, and calcite/dolomite are the principal mineral phases. Enrichment in major elements and depletion in minor elements were observed in studied samples when compared with those of the earth crust. The element contents of coal-bearing layers are similar to those of the US and world coals except for Cd, Li, As and Zn. Based on the calculated enrichment factor, the elements As, Co and Cd are the most pollutants in Parvadeh area. Strong correlations among ash contents and Si, K and Al values indicate that the coal ash is mainly composed of aluminosilicates. Meanwhile, Cd, Co, As, Fe, and S show that Cd, Co, As participated in pyrite lattice. These results were confirmed by factor and cluster analyses. The calculated recovery index shows that Li, Mo, Pb and Cu are bounded to maceral and organic matter thus are enriched in the cleaned coals. The other minor metals, however, are present in mineral part of the coal and enriched in ash.